1. Bohr’s Atomic Theory
Sections 3.3 & 3.4

2. Planck’s Hypothesis
Max Planck ( ) started the quantum revolution by studying light emitted by blackbodies
an ideal black object that does not reflect light but emits light as a result of its temperature
Recall that as you heat a solid it begins to glow – red at first then white.
White light is a combination of all light so the hotter object the more colours of light it emits.
The light intensity can be measured using instruments – produces a curved graph

3. To explain the curve in 1900 Planck came up with a mathematical equation
This equation basically says that light is not continuous but made up of bursts of energy.

4. Einstein further explained the phenomenon by adding that the small bursts were “quanta” (he won the Nobel Prize in 1905)
Quantum (pl. quanta) – a small discrete, indivisible quantity, a quantum of light energy is called a photon.

5. The Photoelectric Effect
The P-E Effect – the release of electrons from a substance sure to light striking the surface of a metal.
Discovered by Heinrich Hertz in 1887
Photon – a quantum of light energy
Each photon of light has a different energy

6. The Big Problem with Rutherford’s Model
Electrons are traveling in a circular orbit always changing directions and is therefore accelerating.
So…if these electrons emitted photons they should lose energy and fall into the nucleus.
Using spectroscopy (analyzing spectra) it was shown that each element has a unique line spectra.

7. A Short Biography
Niels Bohr (b. in Denmark 1885 d. 1962) went to Cambridge University in England and began working with JJ Thompson who, along with his group, was trying to explain electrons in atoms and atomic spectra.
Bohr decided to abandon Thompson’s model and work with the quantum theory of Planck and Einstein.
He went to Manchester and began working with Rutherford
Won the Nobel Prize 1922

8. Bohr’s Theory First Postulate: Second Postulate:
Electrons do not radiate energy as they orbit the nucleus. Each orbit corresponds to a stat of constant energy (called stationary state).
Basically energy states (or levels)
Second Postulate:
Electrons can change their energy only by undergoing a transition from one stationary state to another
Basically, give the electron a quantum of energy and it’ll jump up to the next energy level, when it loses the quantum it falls back down, releasing a photon.